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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Gastridium P. Beauv.

Diminutive of the Greek gaster (belly) referring to the basally swollen glumes.

Type species: Type: G. australe P.Beauv., nom. illeg..

Habit, vegetative morphology. Annual; caespitose (or the culms solitary). Culms 10–60 cm high; herbaceous. Culm nodes glabrous. Culm internodes hollow. Leaves not basally aggregated; vestigially auriculate, or non-auriculate. Leaf blades linear; apically flat; narrow; 1.5–4 mm wide; flat; without cross venation; persistent. Ligule an unfringed membrane; not truncate (veined); 4–6 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence paniculate; contracted; spicate. Primary inflorescence branches borne distichously. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 3–6.5 mm long; compressed laterally; disarticulating above the glumes. Rachilla shortly prolonged beyond the uppermost female-fertile floret (or rarely not prolonged?); the rachilla extension when present, naked. Hairy callus absent. Callus short; blunt.

Glumes two; relatively large; very unequal to more or less equal (the lower somewhat longer); exceeding the spikelets; long relative to the adjacent lemmas (the floret enclosed by their swollen bases); conspicuously ventricose; pointed (acuminate); awnless; carinate; similar (swollen, globular and more or less cartilaginous at the base, membranous above). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas less firm than the glumes; not becoming indurated; incised (more or less dentate); mucronate to awned (the midvein usually excurrent). Awns when present, 1; dorsal; from near the top; geniculate; much shorter than the body of the lemma to much longer than the body of the lemma; entered by one vein. Lemmas hairy, or hairless; non-carinate; 5 nerved. Palea present; relatively long; apically notched; awnless, without apical setae; not indurated (hyaline); 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; glabrous; not toothed. Stamens 3. Anthers 0.5–0.7 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit slightly adhering to lemma and/or palea; small; compressed dorsiventrally (slightly). Hilum short. Embryo small; not waisted. Endosperm hard; with lipid. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Seedling with a short mesocotyl. First seedling leaf with a well-developed lamina. The lamina narrow; erect; 3 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (the costals shorter); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having straight or only gently undulating walls. Microhairs absent. Stomata common; 36–54 microns long. Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare; when present, not paired (solitary); silicified. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (in the furrows); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 7. 2n = 28. 2 ploid. Chromosomes ‘large’.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Agrostidinae. 2 species.

Distribution, phytogeography, ecology. Canaries, western Europe, Mediterranean.

Commonly adventive. Mesophytic to xerophytic; species of open habitats. Grassy places and arable land.

References, etc. Leaf anatomical: this project.

Illustrations. • G. ventricosum: Gardner, 1952. • G. ventricosum (as G. lendigerum): Eng. Bot. (1872). • General aspect (G. phleoides): Gibbs Russell et al., 1990. • Spikelets of G. ventricosum. Gastridium ventricosum. Basally ventricose glumes. • G. ventricosum, abaxial epidermis of leaf blade: this project. • G. ventricosum, abaxial epidermis of leaf blade: this project. • G. ventricosum, TS of leaf blade: this project

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 13th November 2017.’.